Loosening is the major long-term complication of total joint replacement surgery. The previous emphasis on this problem has revolved around studying the mechanical properties of the methylmethacrylate "cement" in current use. We propose to study the problem of prosthesis loosening in living animals, concentrating on the changes that occur at the cement-bone interface to try and relate the role of the methacrylate and the body's response to it in prosthesis loosening. Mechanical factors, infection, heat produced bone death and subsequent remodelling, as well as the possibility of sterile inflammation secondary to methacrylate degradation causing osteolysis will be studied with time as possible factors in prosthesis loosening. All test specimens will be obtained from in vivo implant insertions. Mechanical testing, materials characterization (both chemical and steriological) bacteriological and pathological techniques will be employed.